LECTURES AT JNMCALIGARH MUSLIM UNIVERSITY,ALIGARH

BY: Prof. P N Singh SirCompiled and Uploaded By: Neyaz Ahmad

Contents… Introduction Hemopoiesis Erythropoiesis Classification of Anemia Haemoglobin and Related Disorders WBCs Blood coagulation and Fibrinolytic

system Plasma Proteins ABO classification and Rh factor Diseases…

BloodComposition of bloodCells & Plasma

Cells 1. RBC : Erythroid2. WBC : Myeloid

Neutrophils Basophils Eosinophils

:Lymphoid cellsLymphocytes

: Macrophage system Monocytes

3. Platelets

HemopoiesisCommitted stem cells

Hemopoiesis Pleuripotent hemopoietic stem cell differentiate into Committed stem

cells maturing in a particular cell eg Colony forming unit (CFU)erythrocyte will mature into an erythrocyte . GM-CFU into granulocytes & Monocyte.

Growth promoters like Interleukin-3 induce growth of all the cells in bone marrow.

Differentiation factors like GM –CSF stimulates the differentiation of monocytes and except basophil all the granulocytes.

Lymphocytes are differentiate & mature in Thymus (T cell) / bursal equivalent(B cell) eg liver in mid fetal life & bone marrow in late fetal life & after birth.

ErythropoiesisAreas : yolk sac: primitive embryo Liver :mid gestation Spleen & LN also contribute Bone marrow : After birth & adultStages of erythropoiesis Pleuripotent & Committed

cells ( CFU- E)Proerythoblast: First identifiable cell of series derived

from CFU-E & it give rise basophilic erythroblast (early normoblast) with little Hb. Next generation cell Polychromatophilic erythroblast ( intermidiate normoblast)has Hb saturation of 34% & this gives Orthochromatic erythroblast (Late Normoblast) & subsequently Reticulocyte (Golgi body & mitochondrion turns into reticulum) which disappears within 1-2 days. 1-2 % of circulating RBC are actually reticulocytes.

Early normoblastIntermediate normoblast

Late Normoblast

Red Blood Corpuscle (RBC) RBC : biconcave disk ,7.5 μM diameter

2.5μM thick at periphery , contains 29 pg Hb. 5.4 million/μL (male) 4.8 (Female)in number

Characteristics of RBC

Variable Calculatn

Male Female

Hematocrit 47% 42%RBC Count 5.4 m/μ

L4.8 m/μL

Hemoglobin 16 G% 14 G%Mean Corpuscular Volume (MCV)

Hct x10 RBC count

87 fL 87 fL

Mean Corpuscular Hemoglobin MCH

Hb x10RBCcount

29 pG 29 pG

Mean corp Hb Conc MCHC

Hbx100Hct

34% 34%

Role of erythropoietin, B12 & Folate in Erythropoiesis

Hypoxia causes increase in erythropoietin production from kidney, erythropoietin in turn enhances RBC production

Formation of Erythropoietin. (EP) 90% erythropoietin in kidney 10% in liver. In the kidneys the erythropoietin is formed in tubular epithelial cells.

Ep stimulates hemopoietic stem cell to proliferate into proerythroblast.

Vitamin B12 and folic acid are essential for the synthesis of thymidine triphosphate, & DNA ,hence, deficiency cause failure of nuclear maturation & cell division. The erythroblastic cells of bone marrow, fail to proliferate rapidly, produce macrocytes, with weak cell membrane & oval in shape cells.

Features of Iron, B12 & folate deficiency anemias

Pathology Hemoglobin

RBC Count

MCV MCH MCHC

Iron deficiency

Male< 13.6Female < 12.0 Less

Male <4.3Female 3.5 Less

< 75 μ Lreduced

< 25 pGreduced

< 27 reduced

B12 & folic acid deficiency

Less Less > 110

Normal/ reduced

Normal

Bone marrow

Normoblast Megaloblast

Classification of Anemia according to Underlying Cause Blood Loss Acute: trauma Chronic: lesions of gastrointestinal tract, gynecologic disturbances Defect in RBC

Increased Destruction (Hemolytic Anemias) (A) Intrinsic (intracorpuscular) abnormalities

(a)Hereditary membrane abnormalitiesMembrane skeleton proteins: spherocytosis, elliptocytosis

(b) Hereditory Enzyme deficiencies

Glycolytic enzymes: pyruvate kinase, hexokinase,Enzymes of hexose monophosphate shunt: glucose-6-phosphate dehydrogenase, glutathione synthetase.

Classification by underlying Mechanism Deficiency of dietary factors/ Abnormal Hb Synthesis

Iron : Microcytic Hypochromic

B12 : Macrocytic or Megaloblatic anemia Folic acid : Macrocytic or Megaloblatic anemia

Hereditary Spherocytosis In HS primary abnormality is in

supportive skeleton on IC face of RBC wall. Spectrin, linked to membrane at two points: through ankyrin & band 4.2 to membrane protein band 3; & through band 4.1 to protein glycophorin. Horizontal spectrin - spectrin & spectrin-intrinsic membrane protein interactions stabilize membrane & are responsible for shape, strength, flexibility of RBC.

Hereditary Spherocytosis Most common pathogenic feature of

HS is mutation particularly of band3,ankyrin &spectrin gene. In all types of HS red cell wall stability is reduced , consequently lose membrane fragments while retaining most of their volume. As a result, ratio of surface area to volume of HS cells decreases until the cells become spherical.

Disorders of Hb & RBC production

HemoglobinDeficient globin synthesis :Thalassemia syndrome

Abnormal globin synthesis: Sickle cell anemia RBC production

Failure of erythroblast maturation : B12 & Folate deficiency

Defect of Heme synthesisIron deficiency The most common cause of anemia in India followed by B12 & folate deficiency

Hemoglobin

Hemoglobin is made up of 4 subunits, each have a Heme moiety & polypeptide chain.

HBA has one pair of α & one pair of β globin chain(2α2 β)

HbA2 (2.5%) of Hb has 2α2δ

HbA1c glycated by glucose in diabetics if > 6.9% indicate poor control of blood sugar

Fetal Hb (2α2γ) has more affinity for O2 since it bind less avidly to 2,3-DPG and carries more O2 for a given pO2.

Reactions of Hemoglobin Each of four iron atoms in hemoglobin can reversibly bind one O2

molecule. Iron is in ferrous state, so reaction is oxygenation, not oxidation. Because it contains 4 deoxyhemoglobin (Hb) units,Hb molecule represented as Hb4,& it actually reacts with four molecules of O2 to form Hb4O

Hb4 + O2↔ Hb4O2, Hb4O2+O2 ↔ Hb4O4H b4O4+O2 ↔ Hb4O6 Hb4O6 +O2 ↔Hb4O8 Deoxygenated Hb, globin is tightly bound in tense state so low affinity for O2. Binding of one O2 loosens the binding & increase affinity for O2, 500 times when all 4 Hb are bound with O2

Hemoglobin reactions

Methemoglobin: Oxidizing agent & drugs convert Hb to methHb leading to dusky color of skin. Normally meth hemoglobin formed is converted to Hb by NADH-meth hemoglobin reductase,. Absence of which in children cause congenital methemoglobinemia.

Carboxyhemoglobin: Hemoglobin has more affinity for Carbon monoxide than for O2 which replaces O2 (CO posioning) withreduced O2 carrying capacity of Hb.

Sickle cell anemia In HbS, substitution of valine for glutamic

acid at 6th position of β-chain, produces HbS. Homozygotes all HbA replaced by HbS. Heterozygote about half is replaced. Deoxygenation, HbS molecules crystallize which distort RBC as elongated crescent or sickle. Sickling initially reversible upon reoxygenation; Later on cell wall damage occurs with each episode of sickling, & finally cells accumulate calcium, lose potassium and water, and become irreversibly sickled.

Thalassemia

Inherited disorder caused by mutations that decreases synthesis of α- or β-globin chains. So deficiency of hemoglobin, red cell abnormalities due to excess of other unaffected globin chain. The α chains are encoded by two α-globin genes, which lie in tandem on chromosome 11, while the β chains are encoded by a single β-globin gene located on chromosome 16. The mutations that cause thalassemia are particularly common among Mediterranean, African, and Asian populations.

Beta Thalassemia Pathogenesis of the anemia in β-thalassemia.

Reduced synthesis of β-globin leads to inadequate HbA formation, so RBC MCHC low, cells hypochromic microcytic.

Red cell hemolysis, as results of unbalanced rates of β-globin and α-globin chain synthesis. Unpaired α chains form insoluble aggregates & precipitate in cell & cause membrane damage that is severe enough to provoke extravascular hemolysis. Erythroblasts in bone marrow also susceptible to damage through same mechanism, which in severe β-thalassemia results in destruction of majority of erythroid progenitors before their maturation into RBC. This destruction of erythroid precursors (ineffective erythropoiesis) is associated with an inappropriate increase in absorption of dietary iron, which often leads to iron overload.

Beta Thalassemia

White Blood Cell (WBC)

Human blood contains 4000 to 11,000/μ L WBC Granulocytes (polymorphonuclear leukocytes) are most numerous. Young granulocytes have horseshoe-shaped nuclei that become multilobed as cells grow older. Most of them contain neutrophilic granules (neutrophils), but a few contain granules that stain with acidic dyes (eosinophils), and some have basophilic granules (basophils). Agranulocytes found normally in peripheral blood are lymphocytes, with large round nuclei & scanty cytoplasm, & monocytes, with abundant agranular cytoplasm with kidney-shaped nuclei. Together, these cells provide body powerful defenses against tumors, viral, bacterial, infection &parasitic infestations.

Cell counts

Life span of WBCs & PlateletsCell In

bloodIn tissue

Neutrophil 4-8 hours

4-5 days

Monocyte 10-20 hours

Month (Macrophage)

Platelets 4 day (half life )

Lymphocytes ( blood ↔ lymph lymphoid tissue)

Months -Years

Month -Years

Genesis of myeloid series cells

The promyelocyte which evolves when the classic lysosomal granules, aka primary, or azurophil, granules, are produced. Primary granules contain hydrolases, elastase, myeloperoxidase, cathepsin G, cationic proteins, and bactericidal/ permeability-increasing protein, which kills gram-negative bacteria. Azurophil granules also contain defensins, a family of cysteine-rich polypeptides with broad antimicrobial activity against bacteria, fungi,& certain enveloped viruses. Proliferation phase through metamyelocyte takes about 1 week, & maturation phase metamyelocyte to neutrophil 01 week.

Neutrophils (myeloid cell)

Promyelocyte produce myelocyte, a cell responsible for synthesis of specific, or secondary, granules, containing lactoferrin, vit B12–binding protein, membrane components of NADPH oxidase, required for H2O2 production, histaminase, receptors for certain chemoattractants & adherence-promoting factors (CR3) & receptors for BM component, laminin. During final stages of maturation no cell division occurs, & cell passes through metamyelocyte stage & then to band neutrophil with a sausage-shaped nucleus. During maturation nucleus assumes a lobulated configuration. More lobes seen in folate or vit B12 deficiency. Multiple lobes allow deformation of neutrophils during migration into tissues (Diapedisis).

Bactericidal role of Neutrophils With phagocytosis comes a burst of oxygen consumption and activation of

hexose-mono phosphate shunt. A membrane-associated NADPH oxidase, assembled & catalyzes reduction of O2 to superoxide anion, which is then converted to hydrogen peroxide & other toxic oxygen products (hydroxyl radical).NADPH + H⁺ +2O2= NADP + 2H⁺ + 2O2⁻ (free radical)

2O2 ⁻+ 2H⁺ = H2O2 (in presence of superoxide dismutase)

Hydrogen peroxide + chloride + neutrophil myeloperoxidase generate hypochlorous acid (bleach), hypochlorite, and chlorine. These products oxidize &halogenate microorganisms tumor cells. Strongly cationic proteins, defensins, and probably nitric oxide also participate in microbial killing. Other enzymes, such as lysozyme & acid proteases, digest microbial debris. After 1 to 4 days in tissues neutrophils die.

Eosinophils

Eosinophils express a specific chemoattractant receptor & respond to a specific chemokine, eotaxin. Eosinophils are much long lived than neutrophils, Eosinophils can recirculate. In invasive helminthic infections, such as hookworm, schistosomiasis, strongyloidiasis, toxocariasis, trichinosis, filariasis, echinococcosis, and cysticercosis, the eosinophil plays a central role in host defense. Eosinophils are associated with bronchial asthma, cutaneous allergic reactions, & other hypersensitivity states. Circulating eosinophils are increased in allergic diseases such as asthma & in various other respiratory&gastrointestinal diseases.

Eosinophilic Granules

Eosionphilic granules contain arginine-rich protein (major basic protein)with histaminase activity, important in host defense against parasites. Eosinophil granules also contain a unique eosinophil peroxidase that catalyzes the oxidation of many substances by hydrogen peroxide and may facilitate killing of microorganisms. Eosinophil peroxidase, in the presence of hydrogen peroxide and halide, initiates mast cell secretion in vitro and thereby promotes inflammation. Eosinophils contain cationic proteins, some of which bind to heparin and reduce its anticoagulant activity.

Basophils

Basophils also enter tissues and release proteins and cytokines. They resemble but are not identical to mast cells, and like mast cells they contain histamine and heparin. They release histamine and other inflammatory mediators when activated by a histamine-releasing factor secreted by T lymphocytes and are essential for immediate-type hypersensitivity reactions. These range from mild urticaria and rhinitis to severe anaphylactic shock.

Monocytes

Monocytes enter blood from bone marrow & circulate for 72 hours. They enter tissues & become tissue macrophages. Life span is about 3 months. Do not reenter circulation. Some become multinucleated giant cells seen in chronic inflammations eg tuberculosis. Tissue macrophages include Kupffer cells, pulmonary alveolar macrophages & microglia in brain.

Macrophage activated by lymphokines from T cells. Activated macrophage migrate in response to chemotactic stimuli & engulf kill bacteria by processes similar to as in neutrophils.

They play a key role in immunity. Secrete up to 100 different substances, including factors that affect lymphocytes & other cells, prostaglandins of E series, & clot-promoting factors.

Lymphocytes: To be discussed with Immunity

PlateletsPlatelets are derived from Megakaryocytes in bone marrow Normal count is

1.5 -3.0 lac/cumm of blood, though they do not have nuclei & cannot replicate, function as whole cell.

A. Cytoplasmic active factors (1) Actin and myosin thrombosthenin=contractile proteins. (2) Residuals of endoplasmic reticulum and the Golgi apparatus synthesize

enzymes & store large amount of Ca++. (3).Mitochondria & enzymes capable of forming ATP &ADP. (4) Enzyme systems for synthesis of PG and TxA2 perform many vascular

and other local tissue reactions(5)Fibrin-stabilizing factor,

(6) Growth factor for vascular endothelial cells, vascular smooth muscle cells, and fibroblasts growth, thus causing cellular growth that helps repair damaged vascular walls

B. Membrane factors

(a) Glycoproteins repulses adherence to normal endothelium & causes adherence to injured areas of vessel wall, especially to injured endothelial cells and exposed collagen from deep within the vessel wall.

(b)Phospholipids activate multiple stages in the blood-clotting process. Thus, the platelet is an active structure. It has a halflife in the blood of 8 to

12 days, eliminated mainly by tissue macrophage system. More than one half of the platelets are removed by macrophages in the spleen, where the blood passes through a latticework of tight trabeculae.

Platelet activation

Binding of platelets to injured vessel wall collagen via platelet receptor glycoproteins (GPIa-IIa, & α2β1 integrin) leads to its activation and binding with vWf through another glycoprotein GPIb-V-IX on platelet membrane surface helps in platelet aggregation. This reaction is important in binding of platelet with the vascular endothelium under high shear stress and stenosed arteries. Platelet adherence to endothelium leads to release of contents of dense and α granules. Thrombin which is continuously generated due to continuous use of prothrombin is a stimulus for aggregation for platelets and acts through generation of intra cellular PLCβ that leads to synthesis of intracellular messenger DAG and IP3. DAG stimulates protein kinase C which phosphorylate platelet aggregation protein.

Platelet activation

Platelet activation & Aggregation Thromboxane A2 (Tx A2) is another platelet aggregation factor, synthesis

of which is stimulated by collagen binding. TxA2 is a potent vasoconstrictor of platelet origin like serotonin.

ADP from granules which bind on receptor on platelet and causes activation of platelets. Tx A2 synthesis inhibited by aspirin so it inhibits platelet aggregation. PAF is a potent platelet activation factor produced during glucose metabolism.

All aggregation stimulating factors modify the platelet surface so that divalent fibrinogen link on adjacent platelets by binding with a platelet membrane (integrin IIb-IIIa), autoantibodies against which cause removal of platelet and idiopathic thrombocytopenia.

HemostasisAfter injury to vessels three events stops the

bleeding1. Constriction of vessel (Serotonin TxA22. Temporary hemostatic plug platelet bind

to collagen & aggregate3. Formation of definitive clot (Coagulation of

blood) . The injured vessel contract &may obliterate lumen, vasoconstriction is due to serotonin and other vasoconstrictors liberated (TxA2)from platelets

Coagulation of blood

Platelets in temporary plug bound together & converted to definitive clot by fibrin.

Fibrin formation involves cascade of enzymatic reactions and a series of numbered clotting factors wherein the soluble fibrinogen converted to insoluble fibrin. The process involves the release of two pairs of polypeptides from each fibrinogen molecule. The remaining portion, fibrin monomer, polymerize to form fibrin. The fibrin is initially a loose mesh of interlacing strands. It is converted by the formation of covalent cross-linkages to a dense, tight aggregate (stabilization). This latter reaction is catalyzed by activated factor XIII and requires Ca2+.

Coagulation factors

Coagulation of Blood

Coagulation of blood : Two mechanisms for generation of activated factor X.

Intrinsic & extrinsic : The initial reaction in intrinsic system is conversion of inactive factor XII

to active factor XII (XIIa). This activation, catalyzed by high-molecular-weight kininogen & kallikrein,& can be initiated in vitro by exposing blood to glass, or in vivo by collagen. Active factor XII then activates factor XI, active factor XI activates factor IX. Activated factor IX forms a complex with active factor VIII, which is activated when it is separated from von Willebrand factor. The complex of IXa and VIIIa activate factor X. Phospholipids from aggregated platelets (PL) and Ca2+ are necessary for full activation of factor X.

Extrinsic mechanism of blood coagulation

The extrinsic system is triggered by release of tissue thromboplastin, that activates factor VII. Tissue thromboplastin & factor VII activate factors IX and X. In presence of PL, Ca2+, and factor V, activated factor X catalyzes the conversion of prothrombin to thrombin. The extrinsic pathway is inhibited by a tissue factor pathway inhibitor that forms a quaternary structure with tissue thromboplastin (TPL), factor VIIa, and factor Xa.

Intrinsic & Extrinsic mechanism of Coagulation

Anticlotting Mechanisms

The interaction between platelet-aggregating effect of thromboxane A2 & antiaggregating effect of prostacyclin, which causes clots to form at the site when a blood vessel is injured but keeps the vessel lumen free of clot. Antithrombin III a circulating protease inhibitor binds to serine proteases coagulation system, blocking its activity as clotting factors. The binding is facilitated by heparin, an anticoagulant which is mixture of sulfated polysaccharides. The clotting factors that are inhibited are active forms of factors IX, X, XI, and XII

Fibrinolytic System

Fibrinolytic System

The endothelium of blood vessels also plays an active role in preventing the extension of clots. All endothelial cells except those in cerebral microcirculation produce thrombomodulin, a thrombin-binding protein, on their surfaces. In circulating blood, thrombin is a procoagulant & activates factors V and VIII, but when it binds to thrombomodulin, it becomes an anticoagulant & thrombomodulin–thrombin complex activates proteinC. Activated protein C (APC), along with its cofactor protein S, inactivates factors V and VIII and inactivates an inhibitor of tissue plasminogen activator (tPA), increasing formation of plasmin which activate Plasminogen

Fibrinolytic System

Plasmin (fibrinolysin) is the active component of the plasminogen (fibrinolytic) system. This enzyme lyses fibrin and fibrinogen, with the production of fibrinogen degradation products (FDP) that inhibit thrombin. Plasmin is formed from its inactive precursor, plasminogen, by the action of thrombin and tissue-type plasminogen activator (t-PA). It is also activated by urokinase-type plasminogen activator (u-PA) & a bacterial enzyme Streptokinse.

Fibrinolytic System

Plasminogen receptors are located on the surfaces of many different types of cells and are plentiful on endothelial cells. When plasminogen binds to its receptors, it becomes activated, so intact blood vessel walls are provided with a mechanism that discourages clot formation.

Human t-PA is now produced by recombinant DNA techniques for clinical use in myocardial infarction and stroke.

Coagulation factor deficiency Syndromes

Plasma

The fluid portion of the blood, the plasma , is a remarkable solution containing an immense number of ions, inorganic molecules, and organic molecules that are in transit to various parts of the body or aid in the transport of other substances. Normal plasma volume is about 5% of body weight, or roughly 3500 mL in a 70-kg man. Plasma clots on standing, If whole blood is allowed to clot and the clot is removed, the remaining fluid is called serum. Serum has essentially the same composition as plasma, except that its fibrinogen and clotting factors II, V, and VIII have been removed and it has a higher serotonin content because of the breakdown of platelets during clotting.

Plasma proteins The plasma proteins consist of albumin , globulin , and fi brinogen

fractions. Most capillary walls are relatively impermeable to the proteins in plasma, and the proteins therefore exert an osmotic force of about 25 mm Hg across the capillary wall ( oncotic pressure ) that pulls water into the blood. The plasma proteins are also responsible for 15% of the buffering capacity of the blood because of the weak ionization of their substituent COOH and NH 2 groups. At the normal plasma pH of 7.40, the proteins are mostly in the anionic form (see Chapter 1 ). Plasma proteins may have specific functions (eg, antibodies and the proteins concerned with blood clotting), whereas others function as nonspecific carriers for various hormones, other solutes, and drugs.

ORIGIN OF PLASMA PROTEINS Circulating antibodies are manufactured by lymphocytes. Most of the

other plasma proteins are synthesized in the liver.

Data on the turnover of albumin show that synthesis plays an important role in the maintenance of normal levels.In normal adult humans, the plasma albumin level is 3.5–5.0 g/dL, and the total exchangeable albumin pool is 4.0–5.0 g/kg body weight; 38–45% of this albumin is intravascular, and much of the rest of it is in the skin. Between 6 and 10% of the exchangeable pool is degraded per day, and the degraded albumin is replaced by hepatic synthesis of 200–400 mg/kg/d. Th e albumin is probably transported to the extravascular areas by vesicular transport across the walls of the capillaries Albumin synthesis is carefully regulated. It is decreased during fasting and increased in conditions such as nephrosis in which there is excessive albumin loss.

Plasma Proteins: Physiological fxn & propertiesName Principle

functionBinding characteristic

Serum/Plasma conc.

Albumin Binding and carrier protein;osmotic regulator

Hormones, amino acids, steroids,vitamins, fatty acids

4500–5000 mg/dL

α 1 –Antiprotease

Trypsin and general proteaseInhibitor

Proteases in serum and tissueSecretions

1.3–1.4 mg/dL

α-Fetoprotein Osmotic regulation; bindingand carrier protein

Hormones, amino acids

Found normally in fetal blood

Antithrombin-III

Protease inhibitor of intrinsiccoagulation system

1:1 binding to proteases

17–30 mg/dL

Ceruloplasmin Transport of copper

Six atoms copper/molecule

15–60 mg/dL

Name Principle function

Binding Characteristic

Serum/Plasma Conc.

C-reactive protein

Uncertain; has role in tissue inflammation

Complement C1q

< 1 mg/dL; rises in inflammation

Fibrinogen Precursor to fi brin in hemostasis

200–450 mg/dL

Haptoglobin Binding, transport of cell-free hemoglobin

Hemoglobin 1:1 binding

40–180 mg/dL

Hemopexin Binds to porphyrins, particularly heme for heme recycling

1:1 with heme 50–100 mg/dL

Transferrin Transport of iron

Two atoms iron/molecule

3.0–6.5 mg/dL

Apolipoprotein B

Assembly of lipoprotein particles

Lipid carrier

Angiotensinogen

Precursor to pressor peptide AGII

Name Principal function Binding character

Serum/Plasma conc.

Coagulation factors II, VII, IX, X

Blood clotting 20 mg/dL

Protein C Inhibition of blood clotting

Insulinlike growth factor I

Mediator of anabolic eff ects of GH

IGF-I receptor

Steroid hormone-binding globulin

Carrier protein for steroids in blood

Steroid hormones

3.3 mg/dL

Thyroxine-binding globulin

Carrier protein for thyroid hormone

Thyroid hormones

1.5 mg/dL

Transthyretin (thyroidbindingprealbumin)

Carrier protein for thyroid hormone in bloodstream

Thyroid hormones

25 mg/dL

Blood Groups

ABO system and Rh system are important clinically though 30 common blood groups MNSs, Lutheran, Kell, Kidd, and many others have been identified besides more than 100 rare blood groups. Mismatched transfusion of ABO and Rh sytem cause transfusion reaction hence they will be considered in detail.

The RBC membrane contain blood group antigens, called agglutinogens. The most important are A and B antigens, & Rh(D)antigen

Blood Group: ABO system

A & B antigens inherited as mendelian dominants,& on this basis 4 major blood types . Type A have A antigen, type B have B, type AB have both,& type O have neither. A& B antigens are complex oligosaccharide differing in terminal sugar. An H gene codes for a fucose transferase that adds a terminal fucose, forming H antigen present in all persons. In type A a second transferase add terminal N-acetylgalactosamine on the H antigen,& in type B a transferase add a galactose. In type AB have both transferases present. Individuals who are type O have neither, so the H antigen persists.

Blood Group antigens

Blood Typing

Blood Type & Antigen

Agglutinin in Plasma

Anti sera agglutinates

RBCs agglutinated by plasma of

O Anti A, anti B

None A, B, AB

A Anti B anti A B, ABB Anti A anti B A, ABAB None anti A, anti

B None

Universal Recipient & Donor

Persons with type AB blood are "universal recipients" because they have no circulating agglutinins & can be given blood of any type without transfusion reaction due to ABO incompatibility. Type O individuals are "universal donors" because they lack A and B antigens, & type O blood can be given to anyone without producing a transfusion reaction due to ABO incompatibility. This does not mean, that blood should be transfused without being cross-matched except in most extreme emergencies, since possibility of reactions or sensitization due to incompatibilities in systems other than ABO systems always exists. In cross-matching, donor red cells are mixed with recipient plasma on a slide checked for agglutination.

Rh system

Rh system are also of the greatest clinical importance. The Rh factor, because it was first studied in rhesus monkey named Rh system It is composed of primarily C, D, and E antigens. Rh system has not been detected in tissues other than red cells. D most antigenic component, and the term Rh-positive generally have agglutinogen D. The Rh-negative individual has no D antigen forms anti-D agglutinin when injected with D-positive cells. The Rh typing serum used in routine blood typing is anti-D serum. 85% of Caucasians are D-positive and 15% are D-negative; over 99% of Asians are D-positive.

Transfusion Reactions

Hemolytic transfusion reactions occur when recipient plasma has agglutinins against donor's red cells, cells agglutinate and hemolyze. Free hemoglobin is liberated into plasma. Severity of resulting transfusion reaction may vary from an asymptomatic minor rise in plasma bilirubin level to severe jaundice renal tubular damage leading to anuria & death. However when a recipient has agglutinins against donors RBC, the plasma in transfusion is usually so diluted in the recipient that it rarely causes agglutination even when the titer of agglutinins against recipient's cells is high.

Formation of Anti-Rh Agglutinins.

When red blood cells containing Rh factor are injected into a person whose blood does not contain the Rh factor that is, into an Rh-negative person anti-Rh agglutinins develop slowly, reaching maximum concentration of agglutinins about 2 to 4 months later. This immune response occurs to a much greater extent in some people than in others. With multiple exposures to Rh factor, an Rh-negative person eventually becomes strongly “sensitized” to Rh factor.

Rh Transfusion Reactions.

If an Rh negative person has never before been exposed to Rh positive blood, transfusion of Rh-positive blood into that person will likely cause no immediate reaction. However, anti-Rh antibodies can develop in sufficient quantities during the next 2 to 4 weeks to cause agglutination of those transfused cells that are still circulating in the blood. These cells are then hemolyzed by the tissue macrophage. Thus, a delayed transfusion reaction occurs, although it is usually mild. On subsequent transfusion of Rh-positive blood into same person, who is now already immunized against the Rh factor, transfusion reaction is greatly enhanced and can be immediate and as severe as a transfusion reaction caused by mismatched type A or B blood.

Erythroblastosis & hemolysis in neonate

Another complication due to Rh incompatibility arises when an Rh-negative mother carries an Rh-positive fetus. Small amounts of fetal blood leak into maternal circulation at the time of delivery, & mothers develops anti-Rh antibody. During next pregnancy, mother's agglutinins cross placenta to fetus & cause hemolysis & various forms of hemolytic disease of newborn (erythroblastosis fetalis). If hemolysis severe, infant may die in utero or become anemic, jaundice,& edema (hydrops fetalis). Kernicterus, in which unconjugated bilirubin deposited in basal ganglia if birth is complicated by hypoxia. Bilirubin rarely penetrates brain in adults, but it does in infants ,because BBB is more permeable in infancy. However, main reasons of high unconjugated bilirubin is its increased production &immature bilirubin-conjugating system.

Prevention of Erythroblastosis fetalis

About 50% of Rh-negative individuals are sensitized (develop an anti-Rh titer) by transfusion of Rh-positive blood. Because sensitization of Rh-negative mothers by carrying an Rh-positive fetus generally occurs at birth, first child is usually normal. However, hemolytic disease occurs in about 17% of the Rh-positive fetuses born to Rh-negative mothers who have previously been pregnant one or more times with Rh-positive fetuses. Fortunately, it is usually possible to prevent sensitization from occurring first time by administering a single dose of anti-Rh antibodies. Such passive immunization does not harm mother & has been demonstrated to prevent active antibody formation by mother. This reduces overall incidence of hemolytic disease by more than 90%.